Light responsive system



p 23, 1 J. E. JACOBS 2,853,651

. LIGHT RESPONSIVE SYSTEM Filed Dec. 14, 1953 2 Sheets-Sheet 1 III III

m In (D (D E T .INVENTOR.'-- JOHN E. JACOBS BY.'- H

ATTORNEY Sept. 23, 1958 J, JACOBS I 2,853,651

LIGHT RESPQNSIVE SYSTEM 2 Sheets-Sheet 2 Filed Dec. l4, 1953 INVENTOR.''JOHN E. JACOBS BY! gwaw gy.

ATTORNEY United States Patent" LIGHT RESPONSIVE SYSTEM John E. Jacobs,Milwaukee, Wis., assignor to General Electric Company, a corporation ofNew York Application December 14, 1953,'Serial No. 397,926

Claims. c1. SIS-83) The present invention relates in general toillumination and has more particular reference to the control of lightemitting lamps, especially vehicle headlights, the inventionspecifically pertaining to an improved automatically operable system fordimming vehicle headlights in response to the head-on approach ofanother headlighted vehicle.

An important object of the present invention is to provide control meansautomatically operable to dim the headlights of a vehicle, in responseto the approach of another headlighted vehicle proceeding in theopposite direction, and to restore the vehicle headlights to brightcondition immediately after the approaching vehicle shall have passedby; a further object being to provide automatic headlight controlequipment of simple yet rugged character adapted to furnish trouble-freeoperation during extensive service life; a still further object being toprovide equipment of the character mentioned adapted for readyinstallation and easy interconnection With existing headlight energizingcircuits.

Another important object is to provide an improved photosensitivecontrol system embodying a light detecting element and electricaltranslation means controlled by the detector element and operable inaccordance with the response of the detector to light emitted by theapproaching vehicle for the operation of a relay switch connected in thevehicle lighting system for headlight dimming purposes; a further objectbeing to employ a crystalline semi-conductor material selected from theclass including cadmium sulphide, mercury sulphide, and cadmiumselenide, as a light detecting element for vehicle headlight dimmingpurposes; a still further object being to utilize transistors asamplifying devices in the translation system between the detectingelement and the headlight dimming relay switch.

Another important object is to provide a control system of the sortmentioned for throwing a dimming switch in response to impingement oflight rays at a selected intensity level upon the light detectingelement, for maintaining the system in light dimming condition despitesubstantial reduction in the intensity of light energy caused to impingeupon the detector element, and for reversely throwing the dimming switchupon discontinuation of light impingement on the detector element.

Another important object is to incorporate in the translation system asensitivity offset circuit adapted to change the response level orsensitivity of the system, so that the same may remain in light dimmingcondition after initial actuation of the lamp dimming relay even thoughthe intensity of detector impinging light be reduced below the levelinitially required to cause operation of the relay; a further objectbeing to provide a sensitivity offset circuit adapted, when active, toincrease the sensitivity of the system on the order of eight times thesensitivity of the system when the offset circuit is inactive.

- 'Another important object of the invention is to provide a controlsystem of the sort mentioned, including a light sensitive detector, alamp dimming relay switch,

and a translation system controlled by said detector for actuating theswitch to one position when the detector is dark and to another positionin response to illumination of the detector at above a selectedintensity, and an overriding switch operable to actuate said relayswitch independently of the said detector controlled translation system.

The foregoing and numerous other important objects, advantages, andinherent functions of the invention will become apparent as the same ismore fully understood from the following description, which, taken inconnection with the accompanying drawings, discloses preferredembodiments of the invention.

Referring to the drawings:

Figs. 1 and 2 are diagrammatic showings illustrating the head-onapproach of headlighted vehicles;

Figs. 3 and 4 are diagrammatic representations of light responsivecontrol systems embodying the present invention; and

Fig. 5 is a sectional view through a light sensitive detector deviceemployed in the systems shown in Figs. 3 and 4.

To illustrate the invention the drawings show a vehicle V carrying apair of vehicle headlamps L for projecting beams of light R outwardly ofthe vehicle in which the lamps are mounted. Each of the lamps L mayembody a high or bright beam filament 12 and a low or dim beam filament13, one end of each of said filaments being electrically connected tothe preferably grounded side of a suitable electrical power source 14.The ground remote ends of the high beam filaments may be electricallyinterconnected with one contact 15H of a single pole, double throwdimmer switch 15. The ground remote ends of the low beam filaments mayalso be interconnected with another contact 15L of said dimmer switch,the pole of the dimmer switch being electrically connected with theground remote side of the power source 14, as through suitable circuitprotection devices which may include a disconnecting switch, a fuse, andother desired circut devices, including a meter if desired.

The power source 14 may conveniently comprise a conventional storagebattery of the sort commonly provided as standard equipment inautomotive vehicles for the operation of headlights and other electricalequipment. When the pole of the switch 15 is connected with the powersource 14, it will be seen that the bright and dim beam filarnents 12and 13 may be alternately energized by operation of the dimmer switch15, as by selecheadlights L in response to the head-on approach ofanother headlighted vehicle, such as the vehicle V the present inventioncontemplates alight responsive, electrically actuated translation system20 adapted to energize the relay coil 15C in response to the head-onapproach of said other headlighted vehicle V when the intensity of theheadlight beams R which reach the vehicle V from the headlamps L of theapproaching vehicle V attains a selected lamp dimming level. To thisend, the system 20 may comprise a light sensitive detector 21 mounted inposition to receive the impingement of light rays R emitted by theheadlights of the approaching vehicle, said detector 21 preferablycomprising a semi-conductor material of the electron donor type,particularly crystalline material selected from the class comprisingcadmium sulphide, mercury sulphide,

3 and cadmium selenide. These crystalline semi-conductors exhibit thepower of altering the impedance of their constituent material as afunction of the intensity of light rays impinging thereon. The detector21, accordingly, may be made to control the system 2l in order toenergize the coil 15C when the impedance of the detector reaches apredetermined value in response to the progressively increasing lightintensity applied by the headlight beams R of the approaching vehicleupon the detector 21.

Thelight sensitive crystal detector 21 is preferably sealed within atranslucent, preferably glass envelope E, which may either be evacuatedor else charged with a preferably inert gas, such as nitrogen. Theenvelope B may comprise a cylindrical member formed with an integral,preferably hemispherical closure wall at one end thereof. The crystaldetector 21 may be electrically connected on and'between the ends of apair of spaced apart, electrically conducting support stems S mountedsubstantially parallel within the cylindrical member in positionsupporting the detector 21 substantially at and within thehemi-spherical end closure wall of the envelope E. The stems preferablycomprise metal members capable of being sealed to glass, and said stemsremote from the detector 21 may form glass-to-metal seals with a stemsupporting end closure wall sealing said envelope at the end thereofremote from said hemispherical closure wall. The detector mounting stemsmay extend through and outwardly of said stem supporting end closurewall for connection with the translation system 20. If desired, the stemsupporting end closure wall may also be formed with scalable duct meansD through which the envelope may be evacuatedor charged with inert gas.

The detector enclosing envelope E may be mounted in position presentingthe detector element 21 at the focus of a light collecting reflector C,which may conveniently comprise a parabolic shell formed with internallight reflecting mirror surfaces adapted to deliver, at the focus of thedevice, all light rays entering the open end of theshell. The shell, atits apex, opposite the open end thereof, may be fitted with a mountingsleeve M sized to snugly yet slidingly receive the cylindrical envelopeE, and said envelope may be secured and anchored in the sleeve,presenting the crystal 21 at the focus of the light collecting device C,as by means of any suitable preferably quick drying cement B, such asmalachite basic cement.

The translation system 2% preferably embodies a pair of transistors 22and 23 interconnected to form successive amplifying stages. To this end,each transistor embodies a base element 24, a collector element 25, andan emission element 26, the base of the transistor 22 being connectedWith one side of the detector element 21, the collector of thetransistor 22 being connected with the base of the transistor 23. Thecollector of the transistor 23, in turn, may be connected with one sideof the operating coil 27C of a single pole, double throw relay switch27. The switch 27 may comprise a movable pole electrically connectedwith the ground remote side of the power source 14 and adapted normallyto engage a switch contact 27H, said pole being shiftable to disengagesaid contact 27H and to engage with a contact 27L whenever the operatingcoil 27C is energized. The actuating coil C of the switch 15 may beelectrically connected between ground and the contact 27L of the relayswitch 27. Accordingly, under normal conditions which exist when thecoil 27C is not energized, the switch 27 will be in position engagedwith the contact 27H and disengaged from the contact 27L. The coil 15C,accordingly, also will be (lo-energized, whereby the pole of the switch15 will be engaged with the contact 15H, thus energizing the lamps L forbright beam operation.

As shown more particularly in Fig. .3, the-translation Theinterconnected element 25 of the transistor 22 and the element 24 of thetransistor 23 may be connected with the source of negative potential 28through adjustable resistance means 30 and with the relay switch contact27H through preferably adjustable resistance means 31.

When the light beam R of an approaching vehicle V impinges upon thedetector 21, the impedance thereof will decrease as a proportionalfunction of the intensity of impinging light. The decrease in impedanceallows correspondingly larger amounts of current to flow in the detectorcircuit from the voltage source 23 through the resistor 29, the detector21, thence through the transistor 22 to ground from the base 24 thereof,through the emitter 26 and the ballast resistor 22. This current variesdirectly with the intensity of visible light applied upon the crystaldetector 21 and is substantially zero when the crystal isdark. The flowof current in the detector circuit and through the transistor 22produces corresponding voltage changes at the collector 25 of thetransistor 22, the voltage thus produced at the collector being variablyadiustable by means of the variable sensitivity control resistor 30.Since the collector 25 of the transistor 22 is connected with the base24 of the transistor 23, current flow between the collector 25 andemitter 26 of the transistor 23 will be controlled precisely inaccordance with the voltage fluctuations produced on the collector 25 ofthe transistor 22 as the result of light induced impedance changes inthe detector 21.

The collector 25 and emitter 26 of the transistor 23, however, areinterconnected between ground and the power source 28 in series circuitwith the ballast resistor 23' and the operating coil 27C of the relayswitch 27. The transistors thus, in effect, form a two-stage amplifierfor actuating the relay switch 27 by energizing the coil 27C in responseto light impingement at and above a predetermined intensity value on thedetector 21. Accordingly, when the crystal 21 is dark and thetransistors inoperative to energize the coil 27C, the blade of theswitch 27 will be closed with the contact 27H and open with respect tothe contact 27L. The operatingcoil 15C of the relay switch 15 willaccordingly be inactive and the blade of the switch 15 will be engagedwith the contact 15H, thus connecting the lamps L for bright or highbeam operation. H

As soon as the headlight beams R of an approaching vehicle V impingeupon the detector 21 at a predetermined intensity level, .the system 20may become operative to energize the coil 27C and actuate the switch 27to release its pole from the contact 27H and engage the same with thecontact 27L. Engagement of the pole of the switch 27 with the contact27L completes the energizing circuit of the switch actuating coil 15C,thereby releasing the pole of the switch 15 from the contact 15H andengaging the same with the contact 15L to thus dim the lamps L.

As soon as an approaching vehicle V passes behind the vehicle V,impingement of the beams R upon the detector 21 will be discontinued.When the detector 21 thus becomes dark, the translation system 20,including the transistors 22 and 23, will become inoperative.Accordingly, the switch operating coil 27C will become deenergized, thusallowing the switch 27 to return to its normal position to therebyde-energize the switch actuating coil 150. Theswitch 15-;thus n willbe-allowed to return to its normal position controlling the lamps theswitch 27 is closed with the contact 27H, the voltage developed at thecollector 25 of the transistor 22 will be reduced by the action of theoffset circuit. Such voltage reduction appreciably affects thesensitivity of the translation system, the resistance means 31 being soselected, in conjunction with the operating potentials afforded by thepower sources 14 and 28, so that the sensitivity of the system, when thepole of the switch 27 is disengaged from the contact 27H, may be of theorder of eight times the sensitivity of the system when the pole of theswitch 27 is closed withthe contact 27H.

It is desirable to thus provide for increasing the sensitivity of thesystem in order to avoid flutter or hunting due to recycling of thesystem, in the event that the approaching vehicle V should dim itslights and thus reduce the, intensity at which the same impinge upon thedetector 21 after the switch 27 shall have been actuated to dim thelights L.

The system shown in Fig. 4 is generally similar to that illustrated inFig. 3 in that a pair of transistors 22 and 23 are interconnected as atwo-stage amplifying system for the operation of the relay switch 27 inresponse to the application of light upon the detector 21, theoperation-of the relay switches. 15 and 27 in the Fig. 4 embodimentbeing precisely as described supra in connection with the embodimentshown in Fig. 3. In the Fig. 4 embodiment, however, the emissionelements 26 of the transistors, are connected directly to ground, andthe sensitivity varying offset circuit controlled by the switch contact27H is arranged to function by changing the voltage applied across thedetector 21 when the system is operated to dim the lamps L.

To this end, the transistor remote side of the detector element 21 iselectrically connected, as through a ballast resistor 32, with a powersource terminal 28' preferably providing negative potential of the orderof 125 volts with respect to ground, said transistor remote side of thedetector 21 being also electrically connected through a variableresistor 33 with the switch contact 27H. Accordingly, when the system isin stand-by condition, the detector 21 being dark, the voltage appliedthrough the detector and the transistor 22 comprises the resultant ofthe potential of the power source terminal 28' applied through theresistor 32, as modified by the potential of the power source 14 appliedthrough the switch contact 27H and the adjustable resistor 33. Undersuch conditions the system is sufiiciently sensitive to energize thecoil 27C and dim the lamps L by actuating the switch 27 when theintensity of light impinging on the detector 21 reaches a predeterminedvalue. Upon actuation of the switch 27 in dimming the lamps L, thepoleof the switch 27, in disengaging the contact 27H, will disconnectthe power source 14 from the detector circuit, which thereafter willremain connected only with the power source terminal 28' through theresistor 32. Under such circumstances, the system becomes substantiallymore sensitive so that it will not return or cycle to bright headlightcondition in response merely to the reduction of the intensity ofimpinging light on the element 21, as by the dimming of the headlamps ofthe approaching vehicle V In the system as shown in Fig. 4, thetransistor remote end of the switch actuating coil 27C, as well as thetransistor remote side of the adjustable sensitivity control resistancemeans 30, are both connected with the power source terminal 28, asthrough a resistor 34 sized to provide a negative voltage of the orderof 25'volts with respect to ground at the transistor remote sides of thecoil 27C and of the resistance means 30, said transistor remote sides ofsaid coil 27C and said resistance means 30 being interconnected toground through a resistor 35.

Any suitable or preferred means may, of course, be employed forsupplying power at desired negative potential for the operation of thesystems herein illustrated. As shown more particularly in Fig. 4 of thedrawings, such electrical power at desired negative potential may bedeveloped from the conventional 6 volt power source 14 by means of avibrator device 36, havinga pole electrically connected with the groundremote side of the power source 14 and a pair of contacts 37 adapted tobe alternately engaged by the pole of the vibrator device, said contacts37 being electrically connected with the opposite ends of the primarywinding 38 of a transformer 39, said primary winding having a center tapelectrically connected with the grounded side of the power source 14.

The secondary winding 40 of the transformer 39 may also be provided witha center tap connected to ground, the opposite ends of said secondarywinding being electrically connected, as through rectifiers 41, with thepower source terminal 28'. to thereby deliver the desired negativevoltage with respect to ground at said terminal. If desired, a condenser42 may be electrically connected between the opposite ends of thetransformer winding 40.

In order to allow dimmed lights to be brought to bright condition whilethe detector 21 is illuminated at light dimming intensity, a switch 43may be provided for opening the actuating circuit of the coil 15Cbetween said coil and the contact 27L of the switch 27, therebydeenergizing the coil 15C and allowing the switch 15 to assume itsbright light position, while the coil 27C remains energized and the poleof the switch 27 closed against the contact 27L. The switch 43 thuscomprises an overriding switch for de-energizing the coil 15C in theevent that the oncoming vehicle V should fail to dim its lamps L inresponse to the dimming of the lamps L'.

It is thought that the invention and its numerous attendant advantageswill be fully understood from the foregoing description, and it isobvious that numerous changes may be made in the form, construction andarrangement of the several parts without departing from the spirit orscope of the invention, or sacrificing any of its attendant. advantages,the forms herein disclosed being preferred embodiments for the purposeof illustrating the invention.

The invention is hereby claimed as follows:

1. Control apparatus for automatically dimming vehicle lamps in responseto the approach of another vehicle, comprising relay switch means forcontrolling bright and dim operation of said vehicle lamps and embodyingan operating coil, a photosensitive detector disposed in position to beilluminated by a light beam emitted by the approaching vehicle, atranslation system'embodying a transistor forming an amplifier andhaving a base controllingly associated with said detector, a collectorand means to electrically connect same with a source of electricalenergy through the operating coil of said switch means to energize thesame under the control of said amplifier, andan emitter, means forapplying to said base an electrical bias potential appreciably negativewith respect to said emitter, said relay switch means serving normallyto apply positive electrical potential on said base to thereby reducethe negative value of said bias to a selected level such that said relayswitch means may operate to dim said vehicle lamps in response to lightimpingement on said detector at a selected intensity, said switch meanswhen in light dimming position serving to disconnect said source ofpositive potential from said system to thereby increase the responsesensitivity of the amplifier.

Control apparatus for automatically dimming 've hicle lamps in responseto the approach ofanother vehicle, comprising relay switch means forcontrolling bright and dim operation ofi said vehicle lamps andembodying an operating coil, 8. photosensitive detector disposed'inposition to be illuminated by a light beam emitted by the approachingvehicle, a translation system embodying a pair of transistors forming atwo stage amplifier and each having a base, a collector and an emitter,the base and collector of one transistor being connected respectivelywith said'detector and with the base of the other transistor, means 'toelectrically connect the collector of said other transistor with a saidother transistor being electrically connected with a source ofelectrical energy through the operating coil of said switch means toenergize the same under the control of-said amplifier, the emitters ofsaid transistors being connected to ground, means for applying anelectrical bias potential at a selected level appreciably negative withrespect to ground upon the collector of one transistor and theinterconnected base of the other, said relay switch means servingnormally to apply positive electrical potential on said base to therebyreduce the negative value of said bias potential to a selected levelsuch that said relay switch means may operate to dim said vehicle lampsin response to light impingement on said detector at a selectedintensity, said switch means when in light dimming position serving todisconnect said source of positive potential from said interconnectedcollector and base to thereby increase the response sensitivity of theamplifier.

3. Control apparatus for automatically dimming 'vehicle lamps inresponse to the approach of another vehicle, comprisingrelay switchmeans for controlling bright and dim operation of said vehicle lamps andembodying an operating coil, a photosensitive detector disposed inposition to be illuminated by a light beam emitted by the approachingvehicle, a translation system embodying a transistor forming anamplifier and having a base controllingly associated with said detector,a collector and means to electrically connect same with a source ofelectrical'energy through the. operating .coil of said switch means toenergize the same under the con trol of said amplifier, and an emitter,means including an adjustable resistor for applying to said base anelectrical bias potential appreciably negative with respect to saidemitter, said relay switch means serving normally to apply positiveelectrical potential on said base to thereby reduce the negative valueof said bias to a selected level such that said relay switch means mayoperate to dim said vehicle lamps in response to light impingement onsaid detector at a selected intensity, an adjustable resistorforregulating the value of positive potential applied in said system, saidswitch means When'in light.

dimming position serving to disconnect said source of positive potentialfrom said system to thereby increase the response sensitivity of theamplifier.

4. Control apparatus for automatically dimming vehicle lamps inresponsefio the approach of another vehicle, comprising relay switchmeans for controllingbright and dim operation of said vehicle lamps andembodying an operating coil, a photosensitive detector disposed inposition to be illuminatedby a light beam emittedby the approachingvehicle, a translation system embodying a transistor forming anamplifier and having a base controllingly associated with said detector,a collector and means to electrically connect same with a source ofelectrical energy through the operating coil of said switch means toenergize the same under the control of said amplifier, and an emitter,means for applying to said base an electrical bias potential appreciablynegative with respect to said emitter, said relay switch means servingnormally to apply positive electrical potential on said base to therebyreduce the negative value of said bias to a selected level such-thatsaid relay switch means may operate to dim said vehicle lamps inresponse to light impingement on'said detector at a selected intensity,said switch means when in light dimming position serving to disconnectsaid base from said source of positive potential to thereby increase theresponse sensitivity of the amplifier.

5. Control apparatus for automatically dimming vehicle lamps in responseto the approach of another vehicle, comprising relay switch means forcontrolling bright and dim operation of said vehicle lamps and embodyingan operating coil, a photosensitive detector disposed in position to beilluminated by a light beam emitted by the approaching vehicle,atranslation system embodying a transistor forming an amplifier andhaving a base controllingly associated with said detector, a collectorand means to electrically connect same with a source of electricalenergy through the operating coil of said switch means to energize thesame under the control of said amplifier, and an emitter, means forapplying to said base an electrical bias potential appreciably negativewith respect to said'emitter, said relay switch means serving normallyto connect a source of positive electrical potential with the source ofsaid bias potential tothereby reduce the negative value of said bias toaselected level such that said relay switch means may operate to dim saidvehicle lamps'in response to light impingement on said detector at aselected intensity, said switch means when in light dimmingposition'serving to' disconnect saidsource ofpositive potential fromsaid bias potential source to therebyincrease' the response sensitivityof the amplifier.

References Cited in the file of this patent UNITED STATES PATENTS

